And I'm Melissa Block. Today, evidence of more ugly behavior by American troops in Afghanistan and another round of apologies by U.S. officials. Newly published photographs show soldiers posing with body parts of Taliban suicide bombers. The pictures were taken in 2010 and first reported by The Los Angeles Times. As NPR's Tom Bowman reports, today's revelations can only complicate the war effort.

TOM BOWMAN, BYLINE: The list of incidents continues to grow. Last fall, a two-year-old video surfaced of Marines laughing and urinating on suspected dead Taliban insurgents in Afghanistan. Last month, the murders of 17 Afghan civilians. Now, photographs, soldiers from the 82nd Airborne Division smiling and holding the dismembered legs of a suicide bomber. These pictures were taken two years ago. Defense Secretary Leon Panetta condemned the incident today.

SECRETARY LEON PANETTA: That behavior that was depicted in those photos absolutely violates both our regulations and, more importantly, our core values. This is not who we are, and it's certainly not who we represent when it comes to the great majority of men and women in uniform who are serving there.

BOWMAN: Panetta promised a full investigation. That inquiry might or might not ever answer why these kinds of incidents keep happening. Panetta offered one explanation: war's dehumanizing effect on young troops.

PANETTA: This is war, and I know that war is ugly and it's violent. And I know that young people sometimes caught up in the moment make some very foolish decisions.

BOWMAN: Panetta said there's still no excuse for the behavior. He also raised a more practical problem: whether publication of the photos could lead to violence against U.S. troops.

PANETTA: Neither do I want these images to bring further injury to our people or to our relationship with the Afghan people.

BOWMAN: Such photographs violate military regulations, but are not uncommon in wartime. American soldiers and Marines fighting during World War II - especially in the Pacific - took pictures of enemy dead or body parts. But unlike World War II, Afghanistan is a counterinsurgency. The prize is not an enemy's capital or army, says Nagl, but winning over the people.

LIEUTENANT COLONEL JOHN NAGL: In a counterinsurgency campaign, you're ultimately engaged in a struggle with the insurgents for the support of the population. You're fighting in support of the government of the home nation.

BOWMAN: These kinds of incidents have undermined the U.S. mission before. When American soldiers burned Qurans earlier this year, the Pentagon said it was a mistake. Still, the burnings led to violent protests and the deaths of six U.S. soldiers and a number of Afghan civilians. Nagl also says the latest problems with U.S. troops could also affect public opinion at home.

NAGL: The support of the American people for this war is going to continue to be chipped away by this relentless drip of indications of American soldiers, American Marines not behaving the way we expect them to under extraordinarily difficult circumstances.

BOWMAN: Investigations into the earlier incidents, the Quran burning, the videos of Marines urinating on corpses, have been completed, officials say. So far, no one's been disciplined. Tom Bowman, NPR News, Washington. Transcript provided by NPR, Copyright NPR.